My furnace stopped working last Saturday so I started troubleshooting to find the problem. I found that the board was not providing 110V to my inducer motor. So I determined that I needed a new board. I called a furnace expert to verify my troubleshooting and they discovered that the inducer motor was pulling ~4uA so it needed replaced too. I ordered the parts and replace them. My furnace now works however it is short cycling. Sometimes for just a couple minutes the flame will turn off and they system shut down even though the house is still ~10-15 degrees lower than the set point. Other times it will run for ~10 minutes before this happens. The furnace tries to come back on but never does. I have clean and check the flame sensor to make sure it is pulling the right amount of current and it only shut off after the flame went out. I also check the pressure value and it also only closes after the inducer motor stops. The air filter is new so I don’t really know what else it could be.

The Furnace is ~15 years old and is a Lennox brand.

  • Vacuum detectors for inducer fans sometimes are made with latex/rubber membranes which strect, contact, and allow the gas to flow. The latex/rubber gets old over the years, and not reliably stretchy. You can test for this problem by attaching an alligator clip across the membrane sensor. If the furnace then runs correctly, you need to replace the bypassed sensor. – Wayfaring Stranger Jan 11 '19 at 4:56

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